A server is basically a program that runs on a machine and pro-vides a specific service to all machines that are connected to it. The
you all he can accommodate on a tray. If, however, he doesn’t have
another table. This other waiter passes on the object of desire via
other waiters so it finally ends up on your plate.
Internet users (clients) to access these sites. A Web server is basically
for requests to come around from other machines on the Internet.
request usually ends up at a Web server—unless a proxy server decid-ed that it can help speed up the process by sending you the data itself.
upload and download them from it.
browser, and a real server. It intercepts all requests to the real
❍ A groupware server is software designed to enable users to col-laborate, regardless of location, via the Internet or a corporate
intranet and to work together in a virtual atmosphere.
have been “served” by one when you’ve checked your mail.
❍ A chat server allows you to interact with other users on the net-work in real-time.
The Process Explained—Roughly
To give you a rough sketch of a smooth process, this is what hap-pens when you log on to the Net and type in a URL. The browser you’re using—Internet Explorer, Mozilla Firefox, Safari, Seamonkey,
or anything else—is called a client, which sends a “request” to
access the URL you typed in (say www.yahoo.co.in) to your ISP. The ISP
forwards the request to another (like a file on the table of a typical
government office goes to another table) through the vBNS (the
Very high-speed Backbone Network Services) and so on, until it
reaches the target where the destination is stored—in this case, the
Web site you requested. This “host” computer, or “Web host,” sends
back the packet of data you requested through much the same
channels in much the same way, hopping routers on the way, until
it reaches your ISP. The ISP then sends the data down to your com-puter and the Yahoo! India homepage appears on your screen.
Simple? No. Actually, mucho, muchocomplicated.
The Process Explained—Toughly
We’ll now try to figure out how the Web works by digging a little
deeper and see what exactly happens to get your favourite Web
page on your screen.
Let’s say you typed in the URL of a Web site. The Uniform
Resource Locator, for your convenience, is in letters and numbers,
in recognisable words, so that you can identify and recall it at will.
The computers aren’t human… yet. So, out of our deep sympathy
for the dumb machines, we humans have conceded to talk to com-puters in their language, which is nothing but the language of
numbers. Computers converse with each other in the language of
zeroes and ones—“bits.” If all computers used this binary language
in random ways, exchange of meaningful data would be impossi-ble. To ensure a shared language between two computing
machines, we created “protocols.”
Protocols
A protocol is a set of rules that enables the exchange of information
between two computers, regardless of whether they run on differ-ent operating systems. These rules strictly state the format and pro-cedure to be followed while transmitting data between two com-puters or two networks. A protocol basically gives the “grammar” to their “speech.” Certain key protocols you should know about are:
TCP:Transmission Control Protocol, used for the reliable trans-mission of data over a network.
IP: The Internet protocol is the set of rules that dictates how
exactly packets of data should be transmitted over the Internet.IP
standardises the way machines over the Internet (or any IP net-work) forward or route their packets based on their IP addresses.
HTTP:Hypertext Transfer Protocol, used for transmitting and dis-playing information in the form of Web pages on browsers. This is
the language used when your Web browser talks to the Web server.
FTP:File Transfer Protocol, used for file transfer (uploading and
downloading) over the Internet. Both FTP and HTTP are based on
TCP/IP. FTP is still often used as a means of downloading large files.
SMTP:Simple Mail Transfer Protocol, used for e-mail.
Ethernet: Used for data transmission over a LAN (Local Area
Network).
Wi-Fi:The wireless version of Ethernet.
Of all these protocols, in order to understand how the Internet
works, what we really need to know is the IP and the TCP.
TCP/IP
Every device, every computer, that is part of the Internet, is allo-cated an address, called an Internet address, or Internet Protocol
address (IP address). However, it isn’t like our home address or any-thing because, as we mentioned earlier, computers only under-stand numbers. So the IP address is a series of numbers.
The current protocol is called IPv4. Each IP address is actual-ly just four numbers each ranging from 0 to 255 (each of which
is called an “octet”) and separated by decimal points (called
dots). IP addresses are, therefore in the format xxx.xxx.xxx.xxx
where each xxx could be any number from 0 to 255. So an IP
address could look something like 161.184.138.36. This address
is essential during every exchange of data on the Internet,
because it identifies the client computer (which makes the
request, and to which the data must be sent) and the destination
computer (to which the request must reach). Nothing, therefore,
can happen on the Internet unless your computer is first assigned an IP address.
Say you’ve specified the IP address of a Web site you wish to
access. A server usually has a static IP address. However, your home
PC, if you’re connecting to the Internet through a modem, is usu-ally assigned a different IP address by the ISP each time you dial
in. This IP address is unique to you as a user, but only for as long
as the session lasts. The reason for this system is that ISPs have to
deal with a large number of requests at the same time. Besides, at
any given time, the number of users of the ISP server is limited. To
assign permanent IP addresses to retail users wouldn’t really be
required; instead, ISPs simply allot any IP address that is not being
used at the time to each user who has just dialled in. This system
enables the ISP to get along with fewer IP addresses for the num-ber of users who are connected simultaneously.
TCP breaks down and reassembles packets of data. IP ensures
that the packets are sent to the right destination. The TCP/IP com-bination is used because the Internet is a “packet-switched net-work.” In a “circuit-switched network,” in contrast, once a connec-tion is made, that specific part of the network is exclusively used
only for that connection. In a packet-switched network, the con-nection between the sender and the receiver is not single and
unbroken. When information is sent, it is broken into small pack-ets and sent over many different routes at the same time and then
put together in order at the other end once the packets of data
reach the destination.
How TCP/IP works
Data sent across the Internet is broken up into packets of less than
about 1,500 characters each. Each packet is given a “header,”
which holds the information needed to put the packets back in
right order again. To each header is adder a “checksum”—basical-ly a number that checks whether the precise amount of data in
the packet has been received or not. Each packet is put into what
is called an IP “envelope”—a packet of data with a common address
and other specifications. Once the packets go through the routers
to their destination, TCP, at the receiver’s end, calculates a check-sum for each packet and then compares it with the checksum that was sent in the packet. If these don’t match, the computer figures
that the data has been corrupted en route, discards the packet,
and requests the sender to re-send the packet. TCP then assembles
them into their original coherent form to allow the receiving
computer to make sense of it.
None of this would be possible, however, without a DNS server
acting as mediator.
The Domain Name System
Most of us would find it considerably difficult to remember hun-dreds of strings of numbers of all the sites we visit. So, for humans,
the address is in letters (the URL). The domain name is the root
identifier of a Web site on the Internet.
When you want to contact a location on the Internet—say a Web
site—you’d type in an address like www.yahoo.com. IP uses (a) the
Internet address information and (b) the Domain Name System to
understand and deliver your mail or request from one computer to
another: the letters www.yahoo.comare translated into an IP address,
which is, in this case, 87.248.113.14. In fact, if you typed in
http://87.248.113.14, your screen would show you the Yahoo! site, and
you would make the job a microsecond faster and a trifle easier for
the computers. This translation is accomplished by the DNS server.
Before we understand what the DNS server does, let’s get a grip
of how the DNS works.
How The Domain Name System Works
In order to make efficient and hassle-free the translation from the
plain-English www.yahoo.com into numbers that computers can
understand, the Internet has been organised into a number of
major domains. Major domains are represented by the letters at
the end of the English address. These are called top-level domains
(TLD) or zones, and they are either two or three letters long. The
three-letter zones indicate the type of organisation that owns the
domain, that is, whether it’s a commercial institution, ISP, non-governmental organisation of academic establishment, etc. All
Internet domains are registered with private companies called
Internet Registrars, in co-ordination with the InterNIC (InternetNetwork Information Center). You probably are most familiar with
the .com TLD. Here’s a list:
In October 1998, the Internet Corporation for Assigned Names
and Numbers (ICANN) was formed, and took over the task of managing the domain names and other responsibilities that were ful-filled by the InterNIC. ICANN announced on November 16, 2000,
the following seven new gTLDs:
Besides, additional two-letter domain names have been
assigned to identify domains belonging to particular countries (outside the US)—.au, .in and so on.So that was it .Awaiting for your precious reply